The use of machine tools such as lathes or machining centers typically results in the creation of waste material that desirably should be removed from the object being machined. As used herein, a machining center is a device in which a workpiece, typically a metal object, is held stationary while the cutting portions of the machine tool move around the workpiece to cut and form it into the desired shape or pattern. The term lathe generally refers to a device in which the workpiece rotates while a tool is applied to it. Other types of machine tools can be considered to basically comprise combinations of these two techniques.
In every such case, the metal that is removed from the workpiece is generally removed in rather small pieces that historically have been referred to as chips or coarse solids.
As would be expected, because of the work done by the machine tool on the workpiece the cutting process also creates heat. Accordingly, machine tools such as lathes and machining centers also generally incorporate some sort of cooling system in which a liquid coolant is directed at the workpiece and the appropriate parts of the tool, and then drained from the tool. Because of the expense and usefulness of the coolant, it is generally recaptured and recirculated for further use. As part of the recirculating process, the solid materials generated during the cutting process must be removed from the coolant before it can be recirculated and reused. Historically, such chip material (most often a metal) has been of such a size and density that it would settle out of a fluid relatively quickly. Thus, machine tools generally included sumps to which the coolant and chips it contained were directed. The chips settled to the bottom of the sump, or to a conveying mechanism of some type, from which they could be removed in ordinary fashion.
More recently, extremely high speed tool cutting processes have been developed. For example, spindle speeds presently reach 12,000 rpm or greater. Such high speeds beneficially result in faster processes, higher accuracy in the finished workpiece, and superior surface finishes. As a side effect, however, higher speed processes tend to generate extremely fine solid material rather than the coarse materials typically and previously produced in machining centers and lathes. For example, solid materials as small as 0.005".times.0.010".times.0.020" are typically formed by such newer processes.
Along with higher speeds, the use of lighter (i.e. less dense) alloys is increasing geometrically in this field. When the high speeds and increased accuracy that produce extremely fine solid materials are combined with the lighter alloys, the result is an extremely fine solid material that does not tend to sink from a fluid, but rather floats in it. As stated above, although coarse chip material typically sinks in fluid in a sump where it can be carried off by any convenient mechanism, the fine materials tend to float or "swim" in the coolants. For example, even though most metal particles will eventually settle out of a liquid coolant, the residence time period required for them to do so will be excessive. The practical effect is that these particles must be treated as always floating. Typical sump cleaning devices and methods fail to remove the majority of these fine particles.
Additionally, the lighter alloys often include metals such as aluminum, titanium and magnesium, so that magnetic removal systems that are useful with iron-containing or other magnetically responsive metals or alloys are often useless at removing the fine solids of these lighter alloys.
This raises a number of problems. First, if the extremely fine material is recirculated with the coolant it has obvious detrimental effects on the further cutting processes of the tool. These negative effects include less desirable finishes, relatively poor accuracy, higher wear on the tool, and marred workpieces. The stray chips can also clog fluid lines and valves, thus restricting flow to the workpiece. This reduces the effect of the coolant, and increases the temperature of the workpiece, as well as lowering the lubrication to the tool.
The stray solids can also jam the valves of automatic wheel balancing units used on some grinding machines. Flushing these fluid lines and valves requires that the machine be removed from its normal working operations. The stray solids thus create the need for more frequent cleaning and increase the downtime of the tool.
As another problem, used or "sour" coolants can react with the solid materials to form compounds that tend to float, or gases that encourage the solids to float as the gases effervesce.
The solids cause additional problems with respect to the machine oil (sometimes referred to as "tramp oil") that is almost always present in some amount in most parts of the tool, including its cooling system. Most oils tend to have a negative static charge, while most solid materials produced by the tool tend to have a positive static charge. The opposite charges result in a natural static attraction between oil and solids. Furthermore, the density of the oils and coolants most commonly used in machine tools is such that the oil tends to float upon the coolant. As a result, the solids tend to float with the oil even when the tool is out of operation, and thus they never sink, and in turn never reach conventional sumps and conveyors.
Additionally, even those fine materials which are not recirculated cause problems in that they occupy a great deal of volume within the coolant system. For example, a typical machine tool sump holds about 50 gallons of fluid. To the extent that this volume is filled by solids, two problems can occur: first, a corresponding decrease in available fluid, forcing less fluid to flow more quickly, thus accelerating the residence time problems. Alternatively, the fluid coolant will simply overflow the system.
These consequences in turn reduce the heat sink effect of the coolant in the sump; stated differently, undesireably warmer coolant is returned to the tool.
As yet another problem, the solids are an ideal breeding ground for anerobic bacteria; i.e. the coolant is warm, there may be little circulation, little or no light, and no oxygen supply to discourage such bacteria. Such bacteria tend to attack and break down the coolant, shortening its operational life. In extreme cases, such bacteria can be persistent enough that the entire machine tool must be sterilized.
In almost all of these cases, the machine tool has to be stopped frequently to address the particular problem, such as removing enough of the fine materials to make sure that enough coolant volume remains for the appropriate cooling purposes. The corresponding "down time" presents a significant disadvantage. In some cases a down time of up to 12 hours is required for cleaning the tool every third or fourth operating day.
Present attempts at solving the problem of additional fine solid materials in the machine tool industry typically comprise the use of separate, stand-alone systems distinct from the machine tool itself. This, however, raises a number of problems. First, the coolant must pass from the machine tool to separate, external devices such as conveyors, filters or coalescors to filter and clean the coolant. Because separate components are required, additional floor space and duplicate drive systems for each individual component are correspondingly required. As is known to those in the machine tool industry, floor space is generally at a premium and therefore such expensive and space consuming auxiliary components are disadvantageous.
A typical solution to the problem is set forth in U.S. Pat. No. 4,895,647 to Uchiyama. Such a device, however, in addition to dictating additional floor space, also requires that all of the coolant be transferred externally from the machine tool to the device, cleaned, and then returned to the machine tool, all in the absence of any leaks or other problems. As might be expected, this raises significant difficulties in the overall process, with accompanying costs and other disadvantages. Perhaps most significantly, devices such as suggested by Uchiyama absolutely require arrangements to prevent any coolant from reaching the sump originally designed for and included within the machine tool.
Furthermore, devices such as that described by Uchiyama that attempt to deal with fine solids generally cannot remove the coarse solids that are still produced during many typical processes. Therefore, the fine solid removal system must still be accompanied by some other system for removing coarse materials.